Polysaccharides depolymerization via hydroxyl radicals attack in dilute aqueous solution

The time course of the depolymerization of pullulan, carboxymethylcellulose, welan, scleroglucan and scleroglucan ionic derivatives (''sclerox'') in dilute aqueous solution of hydroxyl free radicals (*OH) has been monitored by means of viscosity measurements at 20 degrees C. Two *OH sources have been employed, namely: Cu(II)/ascorbate and N-hydroxy-2-thiopyridone. Singly dispersed polysaccharidic chains undergo depolymerization at a relatively high rate which appears to depend only scarcely on chain structure and charge density, for the experimental conditions employed. Conversely, chains in double-stranded form (welan) or in triple-stranded form (scleroglucan) exibit viscosity decreases which are very small (welan) or undetectable (scleroglucan) whithin the first 1-2 hours of measurements. However, single strands scissions due to *OH attack become manifest when welan and scleroglucan solutions undergo thermal cycles following which their viscosity irreversibly decreases by as much as 70% with respect to that of the initial states.